Hot water supply apparatus

ABSTRACT

According to the hot water supply apparatus of the present invention, it becomes possible to effectively prevent the dew condensation on a bypass line. While exhaust gas after passage through a heat exchanger  2  is passing through an exhaust gas collection section  14  and then through an exhaust gas tube  15,  combustion air in the inside of an inlet air tube  16  and a supply air collection section  17  is heated by heat exchange. A bypass line  19  which connects together a water supply line  3  and a hot water supply line  5  is disposed so as to pass through a clearance  20  defined between a supply air duct  18  which supplies heated combustion air to an air sending fan  6  and a burner casing  10  whereby the bypass line  19  is heated by the heat of combustion air in the inside of the supply air duct  18.  Alternatively, the bypass line  19  may be disposed and placed so as to pass through the inside of the supply air duct  18.

TECHNICAL FIELD

The present invention relates to a hot water supply apparatus provided with a bypass line which establishes fluid communication between a water supply line and a hot water supply line and more particularly, relates to technology intended for the prevention of the dew condensation on the bypass line.

BACKGROUND ART

Heretofore, there has been proposed a hot water supply apparatus. In this hot water supply apparatus, a water supply line which is connected to the inlet side of a heat exchanger and a hot water supply line which is connected to the outlet side thereof are connected together by a bypass line, whereby the entry amount of water to be supplied to the heat exchanger is reduced by an amount of water to be bypassed by the bypass line, thereby further raising the temperature of hot water from the heat exchanger and in addition, it is also intended that the heat exchanger is prevented from the dew condensation thereon by increasing the hot water temperature (see, for example, Patent Literature 1).

In addition, there has been a proposal in which a large number of bristles (hairs) formed of plastic fiber are implanted onto the outer surface of a water supply line through which water is admitted to a heat exchanger, whereby it is intended that the outer surface of the water supply line is prevented from the dew condensation thereon (see, for example, Patent Literature 2)

Citation List Patent Literature

-   Patent Literature 1: JP-A-2005-265365 -   Patent Literature 2: JP-UM-A-63 (1988)-168760

SUMMARY OF INVENTION Technical Problem

Incidentally, cold water flows also into the bypass line from the water supply line and then flows in the direction of the hot water supply line, so that it is likely that the outer surface of the bypass line will also undergo the dew condensation thereon. Especially, in the case where the water supply line and the hot water supply line are disposed at a distance from each other with the heat exchanger sandwiched therebetween, the length of extension of the bypass line for connecting together these lines inevitably increases and as a result, the possibility that the dew condensation takes place will increase and in addition, the area where the dew condensation occurs will expand.

For example, in the case where the heat exchanger is a fin and tube type heat exchanger which is composed of a large number of fins and a plurality of tubes which pass completely through these fins, the tubes of the heat exchanger are arranged such that they pass completely through the many fins and then turn back so as to repass through the fins. In this case, if the number of tubes to be passed through the fins is set not at an even number but at an odd number, this results in that the tube's starting point to which the water supply line is connected and the tube's end point to which the hot water supply line is connected are located on sides opposite to each other across the heat exchanger. As a result of this, it is required that the bypass line for connecting together the water supply line and the hot water supply line also be arranged so as to pass transversely across a can body in which the heat exchanger and so on are housed and as a result, the length of extension of the bypass line becomes relatively long.

With this situation in mind, the present invention was developed. Accordingly, an object of the present invention is to provide a hot water supply apparatus capable of effectively preventing the dew condensation, particularly, on the bypass line.

Solution to Problem

In order to achieve the aforesaid object, a hot water supply apparatus according to a first invention comprises: a heat exchanger which is heated by heat exchange with the heat of combustion from a combustion burner; a water supply line for flow of water through the heat exchanger; a hot water supply line through which hot water heated by passage through the heat exchanger is supplied; a bypass line which connects together the water supply line and the hot water supply line so that the heat exchanger is bypassed; an air sending fan which sends combustion air to the combustion burner; and a supply air pathway section which supplies, to the air sending fan, combustion air heated by heat exchange with exhaust gas in the inside of an exhaust gas pathway section for discharge of exhaust gas from the combustion burner. In the hot water supply apparatus of the first invention, at least a part of the bypass line is disposed and placed so as to pass through a position located close to a supply air duct which forms the supply air pathway section.

For the case of the first invention, the outer surface of the bypass line receives, through the wall of the supply air duct, heat radiation from heated air in the inside of the supply air duct whereby the outer surface of the bypass line is heated. Therefore, even when cold water from the water supply line flows through the inside of the bypass line, the outer surface of the bypass line is prevented from the dew condensation thereon. Furthermore, it becomes possible to utilize the heat of combustion air heated by heat exchange with exhaust gas, to thereby prevent the bypass line from the dew condensation thereon. Because of this, it becomes possible to intend to prevent the dew condensation without any extra countermeasure such as a special process of, for example, implanting a large number of bristles on the outer surface of the bypass line.

For the case of the first invention, it may further be arranged such that the bypass line is disposed and placed so as to pass through a clearance defined between the supply air duct and a casing of the combustion burner. The clearance defined between the supply air duct and the casing of the combustion burner is maintained in a state of relatively high temperature by being affected by heat from both of the preheated air in the inside of the supply air duct and the burned gas in the inside of the casing of the combustion burner, for as long as the apparatus is in a hot water supply operation mode (combustion operation mode). Therefore, by such an arrangement that the bypass line is disposed and placed in the clearance maintained in a high temperature state, the prevention of the dew condensation is more effectively achieved.

In addition, a hot water supply apparatus according to a second invention comprises: a heat exchanger which is heated by heat exchange with the heat of combustion from a combustion burner; a water supply line for flow of water through the heat exchanger; a hot water supply line through which hot water heated by passage through the heat exchanger is supplied; a bypass line which connects together the water supply line and the hot water supply line so that the heat exchanger is bypassed; an air sending fan which sends combustion air to the combustion burner; and a supply air pathway section which supplies, to the air sending fan, combustion air heated by heat exchange with exhaust gas in the inside of an exhaust gas pathway section for discharge of exhaust gas from the combustion burner. In the hot water supply apparatus of the second invention, at least a part of the bypass line is disposed and placed so as to pass through a wall of a supply air duct which forms the supply air pathway section and then through the inside of the supply air duct.

For the case of the second invention, since the bypass line is disposed and placed so as to pass through an internal space in the inside of the supply air duct in which combustion air flows, this allows the bypass line to more directly receive heat radiation/heat conduction from the combustion air, thereby making it possible to intend to further make sure that the dew condensation is prevented, in addition to obtaining the same operation as obtained in the case of the first invention.

In addition, in either the first invention or the second inventions, the bypass line may be disposed and placed in a position lower than a flange which forms an upper end opening edge of the casing of the combustion burner. As a result of such arrangement, even in the unlikely event of the formation or the dropping of condensation water, it becomes possible to avoid the possibility of the occurrence of inconveniences due to the condensation water. That is, it is possible that if condensation water falls onto the flange of the casing of the combustion burner, the condensation water will circulate around the flange. This causes the inconvenience that the condensation water may fall in such a spreading state that it is impossible to tell where it will fall. However, because of the aforesaid arrangement that the bypass line underlies the flange, it becomes possible to definitely avoid the occurrence of the aforesaid inconvenience even if condensation water falls, thereby making it possible to prevent the occurrence of situations where various electronics devices become wet by condensation water.

In addition, in either the first invention or the second invention, a part of the exhaust gas pathway section and a part of the supply air pathway section are in the form of a double tube structure composed of an inner tube and an outer tube whereby the heat exchange with exhaust gas is performed. This ensures that combustion air is heated by heat exchange with exhaust gas in the exhaust gas pathway section and consequently, it becomes possible to further ensure that the operation of intending to prevent the dew condensation by heating the bypass line with combustion air in the inside of the supply air duct in the present invention, can be accomplished.

Advantageous Effects of Invention

As has been described above, according to the hot water supply apparatus of the first invention, it is possible to heat the outer surface of the bypass line by use of the heat of combustion air thermally radiated through the wall of the supply air duct, thereby making it possible to make sure that even if cold water from the water supply line flows into the inside of the bypass line, the outer surface thereof is prevented from the dew condensation thereon. Furthermore, the heat of combustion air heated by heat exchange with exhaust gas can be used to prevent the bypass line from the dew condensation thereon, because of which it becomes possible to intend to prevent the dew condensation without addition of any special process, such as, for example, a process of implanting a large number of bristles on the outer surface of the bypass line.

Especially, by the arrangement that the bypass line is passed through a clearance defined between the supply air duct and the casing of the combustion burner, the prevention of the dew condensation can be accomplished more effectively in the clearance maintained in a state of relatively high temperature by the effect of heat from both the combustion air in the inside of the supply air duct and the burned gas in the inside of the casing of the combustion burner.

According to the hot water supply apparatus of the second invention, the bypass line is disposed and placed so as to at least partially pass completely through the wall of the supply air duct which forms the aforesaid supply air pathway section, thereby passing through the inside of the supply air duct. This allows the bypass line to receive, in a more direct manner, heat radiation/heat conduction from the combustion air in the inside of the supply air duct. Because of this, it becomes possible to intend to further ensure that the preventing of the dew condensation is accomplished.

If, in either the first invention or the second invention, the bypass line is disposed and placed so as to underlie a flange which forms an upper end opening edge of the casing of the combustion burner, this makes it possible to definitely avoid, even in the unlikely event of the generation of condensation water or the dropping thereof, such an unexpected situation that the generated condensation water falls in a spreading state. This makes it possible to prevent the occurrence of a situation where various electronics devices become wet by condensation water.

In addition, if, in either the first invention or the second invention, a part of the exhaust gas pathway section and a part of the supply air pathway section are formed in the form of a double tube structure composed of an inner tube and an outer tube for enabling heat exchange with exhaust gas, this more definitely accomplishes the heating of combustion air by heat exchange with exhaust gas in the inside of the exhaust gas pathway section. Consequently, it becomes possible to further ensure that the effect of the present invention to intend to prevent the dew condensation by heating the bypass line with combustion air is achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an embodiment of a hot water supply apparatus of the present invention.

FIG. 2 is an explanatory diagram showing a more concrete structure (with a housing omitted) of a hot water supply apparatus as belonging to the aforesaid embodiment, when viewed from the rear side.

FIG. 3 is an explanatory diagram in cross section taken along line A-A of FIG. 2.

FIG. 4, comprised of FIG. 4( a), FIG. 4( b) and FIG. 4( c), is a partially enlarged diagram of FIG. 3 showing the concrete positional relationship between a bypass line and a supply air duct wherein FIG. 4( a) is an example of the proximate arrangement shown by way of example in FIG. 3, FIG. 4( b) is an example of the contact arrangement and FIG. 4( c) is an example of the internal pass-through arrangement.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be described based on the drawing figures.

FIG. 1 shows a principled hot water supply apparatus according to an embodiment of the present invention. This hot water supply apparatus is configured such that water admitted from a water supply line 3 is heated by heat exchange with the combustion heat of a combustion burner 4 during passage through the inside of a heat exchanger 2, whereby hot water heated up to a predetermined temperature is delivered through a hot water supply line 5. The heat exchanger 2, shown by way of example in the figure, is formed by a fin and tube type heat exchanger and is configured such that water taken in from the water supply line 3 is heated by heat exchange with burned gas (to be hereinafter described) while it is being turned back in a plurality of tubes to finally reach the hot water supply line 5. The combustion burner 4 is configured such that a mixture of combustion air from an air sending fan 6 and gas as a fuel supplied from a gas supply section 7 is burned and the resulting burned gas is, after passage through the heat exchanger 2, discharged to the outside via the exhaust gas pathway section 8 as exhaust gas. It is arranged such that air is introduced through the supply air pathway section 9 into the air sending fan 6 from the outside, and the supply air pathway section 9 is located partially adjacent to the exhaust gas pathway section 8 whereby air in the inside of the supply air pathway section 9 is heated by heat exchange with exhaust gas in the inside of the exhaust gas pathway section 8.

The combustion burner 4 is contained within a burner casing (combustion burner casing) 10 which it's upper end is opened. The heat exchanger 2 is contained within a heat exchanger casing 11 which is adapted to open vertically. The heat exchanger casing 11 is placed on a burner casing flange 12 serving as a flange which forms an upper end opening edge of the burner casing 10 and is connected therewith. Furthermore, a supply-exhaust structural section 13 is placed atop the heat exchanger casing 11 and is connected therewith.

The supply-exhaust structural section 13 is composed of: an exhaust gas collection section 14 which covers the upper side of the heat exchanger 2 to thereby gather exhaust gas after passage through the heat exchanger 2; an exhaust gas tube 15 which guides exhaust gas collected in the exhaust gas collection section 14 out to a predetermined discharge area; an inlet air tube 16 which forms an outer tube enclosing around the outer circumference of the exhaust gas tube 15 as an inner tube; and a supply air collection section 17 which is formed as a partition so as to cover the exhaust gas collection section 14 to thereby gather air introduced from the inlet air tube 16. The exhaust gas tube 15 and the inlet air tube 16 are disposed and placed to be formed in the form of an inner-outer double tube structure whereby air in the inside of the inlet air tube 16 situated on the outer side is heated up to a predetermined temperature (for example, 80 degrees Centigrade) by heat exchange with the heat of exhaust gas in the inside of the exhaust gas tube 15 situated on the inner side. And, a supply air duct 18 is disposed and placed such that it extends, along the side of the heat exchanger casing 11 and along the side of the burner casing 10, from the supply air collection section 17 to the air sending fan 6 whereby combustion air in a heated state is introduced from the supply air collection section 17 by way of the supply air duct 18. The exhaust gas pathway section 8 is composed of the exhaust gas collection section 14 and the exhaust gas tube 15, and the supply air pathway section 9 is composed of the inlet air tube 16, the supply air collection section 17 and the supply air duct 18. Stated in another way, the supply air pathway section 9 corresponds to a section which is formed in the form of a double tube structure and at which heat exchange with exhaust gas is performed.

On the other hand, the water supply line 3 is connected, at its upstream end, to a supply water line (not shown in the figure) whereby water supplied at a predetermined supply water pressure from the supply water line is admitted to the heat exchanger 2. In addition, the hot water supply line 5 is connected, at its downstream end, to a hot water supply line (not shown in the figure) whereby hot water is supplied through the hot water supply line to hot water supply taps in the kitchen, the washroom, the bathroom and so on. And, the upstream end of a bypass line 19 is connected so as to bring into branching connection with the water supply line 3 at a position short of the heat exchanger 2, and the downstream end of the bypass line 19 is connected so as to come into connection with the hot water supply line 5 at a position thereof along the way. That is, water taken in from the water supply line 3 is made to bypass the heat exchanger 2 by means of the bypass line 19, thereby making it possible to provide a bypass supply of water taken in from the water supply line 3, directly to the hot water supply line 5.

After branching off from the water supply line 3, the bypass line 19 is disposed and placed as follows. That is, the bypass line 19 passes through a position near the wall of the supply air duct 18 (i.e., a position in a clearance 20 defined between the supply air duct 18 and the burner casing 10) so that it is connected to the hot water supply line 5. In other words, the outer surface of the bypass line 19 is heated by receipt of heat radiation from combustion air through the wall of the supply air duct 18, thereby preventing the dew condensation on the outer surface of the bypass line 19 through which cold water flows. Besides, by being affected by heat from both of the combustion air in a heated state in the inside of the supply air duct 18 and the burned gas in the inside of the burner casing 10, the clearance 20 defined between the supply air duct 18 and the burner casing 10 serving as a space through which the bypass line 19 passes is maintained in a state of relatively high temperature for as long as the apparatus is in a hot water supply operation mode (combustion operation mode), so that the prevention of the dew condensation is more effectively accomplished. In addition, the bypass line 19 and various electronics devices are laid out such that neither the electronics devices (for example, the motor of the air sending fan 6, the electromagnetic valve of the gas supply section 7 and other like device) nor the electronics devices such as various sensors and so on are located underlying the bypass line 19 while on the other hand, the bypass line 19 is disposed and placed so as to pass transversely under the burner casing flange 12. Because of this, even in the unlikely event that condensation water falls from the bypass line 19, the condensation water will not fall onto the various electronics devices. This ensures that one of the problems associated with the prior art techniques (i.e., the situation where condensation water falls in a spreading state onto the burner casing flange 12 and circulates therearound, thereby making it impossible to tell where the dew water falls) can be avoided.

And, when the hot water supply tap is turned on and water at more than a predetermined flow rate is admitted from the water supply line 3 on the basis of the supply water pressure, the air sending fan 6 is operated and the combustion burner 4 is operated to burn. And, hot water heated up to a predetermined temperature is drawn off to the hot water supply line 5 from the heat exchanger 2. Then, the hot water is supplied to the hot water supply tap at the downstream end. In this hot water supply operation, because of the operation of the air sending fan 6 (formed by, for example, a sirocco fan, a turbo fan or other like fan), outside air is introduced through the inlet air tube 16 and then collected in the supply air collection section 17. Subsequently, the air is introduced through the supply air duct 18 into the air sending fan 6 and then supplied to the combustion burner 4 as combustion air. And exhaust gas generated by combustion in the combustion burner 4 is discharged from the exhaust gas collection section 14 through the exhaust gas tube 15. By heat exchange between the supply (the combustion air) and the exhaust (exhaust gas), combustion air is heated in the supply-exhaust structural section 13, as has been described above, and the heat of the combustion air in a heated state can further be utilized for preventing the bypass line 19 from the dew condensation thereon. Because of the above, it becomes possible to intend to prevent the dew condensation by making efficient use of exhaust heat, without addition of any special process such as, for example, a process of implanting a large number of bristles on the outer surface of the bypass line.

In addition, any of the following can be employed as a position at which the bypass line 19 is disposed and placed on the relationship with the supply air duct 18. That is to say, (1) the bypass line 19 is disposed and placed not in contact with but adjacent to the supply air duct 18; (2) the bypass line 19 is fixed in contact with the supply air duct 18; or (3) the bypass line 19 is disposed and placed such that it is passed through the wall of the supply air duct 18 so as to pass through the inside of the supply air duct 18, can be employed.

Next, referring to FIGS. 2 and 3, a description will be given in regard to a more concrete example of the hot water supply apparatus shown in FIG. 1. In the following description, the constituent elements are assigned the same reference numerals as their counterparts shown in FIG. 1. However, it should be noted that each of the constituent elements of the hot water supply apparatus shown by way of example in FIGS. 2 and 3 is just merely one concrete example of each of the constituent elements of the hot water supply apparatus shown in FIG. 1. In both the figures, reference numeral 21 denotes a main body casing of the hot water supply apparatus and reference numeral 22 denotes a front cover for closing a front opening section of the main body casing.

The supply-exhaust structural section 13 of the hot water supply apparatus shown by way of example in FIGS. 2 and 3 is configured as follows. That is, the exhaust gas pathway section 8 is composed of the exhaust gas collection section 14 which covers the upper end opening of the heat exchanger casing 11 and the exhaust gas tube 15 which extends upward from the exhaust gas collection section 14 while on the other hand, the supply air pathway section 9 is composed of the supply air collection section 17 which is placed so as to further cover the exhaust gas collection section 14 from above, the inlet air tube 16 which extends upward from the supply air collection section 17 and which covers the outer circumference of the exhaust gas tube 15 to thereby be formed in the form of a double tube structure and the supply air duct 18 whose upstream end is brought into fluid communication with the supply air collection section 17 through a laterally-expanded communication aperture 181 and whose downstream end is brought into fluid communication with the air sending fan 6 through a communication aperture 182. The supply air duct 18 is formed as a duct whose upstream end side (upper side) extends so as to have the same width as the supply air colleting section 17 when viewed from the rear surface side of the main body casing 22 (see FIG. 2) and whose downstream end side (lower side) has an inverted triangular, flattened shape tapering toward the communication aperture 182 with the air sending fan 6 (see FIG. 3).

And, the fin and tube type heat exchanger 2 is configured having an odd number of tubes whereby with respect to the direction in which the tubes are disposed and placed, the water supply line 3 and the hot water supply line 5 extend vertically, in a respectively place where the water supply line 3 arranged on one of the right- and the left-hand sides of the heat exchanger casing 11 and where the hot water supply line 5 arranged on the other of the right- and the left-hand sides of the heat exchanger casing 11. The bypass line 19 which connects together the water supply line 3 and the hot water supply line 5 at their intermediate positions relative to the vertical direction, is disposed and placed so as to pass transversely in the horizontal direction at a position which is located not only in the clearance 20 (see FIG. 3) between the supply air duct 18 and the burner casing 10 but also lower than the burner casing flange 12.

The concrete positional relationship between the bypass line 19 and the supply air duct 18 may be as follows: as shown in FIG. 4( a), the bypass line 19 is disposed in the vicinity of a wall 183 of the supply air duct 18 (not in contact with the wall 182 but at a very small distance away therefrom); as shown in FIG. 4( b), the bypass line 19 is fixedly disposed in contact with the wall 183 of the supply air duct 18; or as shown in FIG. 4( c), the bypass line 19 is disposed such that it is passed through the wall 183 of the supply air duct 18 to thereby pass through the internal space of the supply air duct 18.

The operation/working effect of the hot water supply apparatus shown by way of example in FIGS. 2 and 3 is the same as the operation/working effect of the hot water supply apparatus of FIG. 1 as described above. However, for the case of the hot water supply apparatus of FIGS. 2 and 3, the distance for which the bypass line 19 runs side by side with the supply air duct 18 can be made relatively long whereby it becomes possible to achieve more effectiveness in the light of the prevention of the dew condensation.

In addition, the present invention is not limited to the foregoing embodiments and therefore includes other various embodiments. That is, the supply air duct 18 can selectively be formed into any shape whatsoever as long as combustion air can be introduced to the air sending fan 6. And, the bypass line may be disposed so as to pass transversely across the supply air duct in the horizontal direction depending on such a selection of shape and in addition, the bypass line may be curved along the way to be configured so as to have a portion that extends vertically, a portion that passes obliquely or other like portion. In addition, other than being formed in the form of a double tube structure, the supply-exhaust structural section 13 may employ a structure in which a part of the exhaust gas pathway section 8 and a part of the supply air pathway section 9 are brought into contact with each other whereby combustion air is heated by receipt of the heat conducted from the exhaust gas. 

1. A hot water supply apparatus comprising: a heat exchanger which is heated by heat exchange with the heat of combustion from a combustion burner; a water supply line for flow of water through said heat exchanger; a hot water supply line through which hot water heated by passage through said heat exchanger is supplied; a bypass line which connects together said water supply line and said hot water supply line so that said heat exchanger is bypassed; an air sending fan which sends combustion air to said combustion burner; and a supply air pathway section which supplies , to said air sending fan, combustion air heated by heat exchange with exhaust gas in the inside of an exhaust gas pathway section for discharge of exhaust gas from said combustion burner; wherein at least a part of said bypass line is disposed and placed so as to pass through a position located close to a supply air duct which forms said supply air pathway section.
 2. The hot water supply apparatus as set forth in claim 1 wherein: said bypass line is disposed and placed so as to pass through a clearance defined between said supply air duct and a casing of said combustion burner.
 3. The hot water supply apparatus as set forth in claim 2 wherein: said bypass line is disposed and placed in a position lower than a flange which forms an upper end opening edge of said casing of said combustion burner.
 4. The hot water supply apparatus as set forth in claim 2 wherein: a part of said exhaust gas pathway section and a part of said supply air pathway section are formed in the form of a double tube structure composed of an inner tube and an outer tube whereby said heat exchange with exhaust gas is performed.
 5. The hot water supply apparatus as set forth in claim 3 wherein: a part of said exhaust gas pathway section and a part of said supply air pathway section are formed in the form of a double tube structure composed of an inner tube and an outer tube whereby said heat exchange with exhaust gas is performed.
 6. A hot water supply apparatus comprising: a heat exchanger which is heated by heat exchange with the heat of combustion from a combustion burner; a water supply line for flow of water through said heat exchanger; a hot water supply line through which hot water heated by passage through said heat exchanger is supplied; a bypass line which connects together said water supply line and said hot water supply line so that said heat exchanger is bypassed; an air sending fan which sends combustion air to said combustion burner; and a supply air pathway section which supplies, to said air sending fan, combustion air heated by heat exchange with exhaust gas in the inside of an exhaust gas pathway section for discharge of exhaust gas from said combustion burner; wherein at least a part of said bypass line is disposed and placed so as to pass through a wall of a supply air duct which forms said supply air pathway section and then through the inside of said supply air duct.
 7. The hot water supply apparatus as set forth in claim 6 wherein: said bypass line is disposed and placed in a position lower than a flange which forms an upper end opening edge of said casing of said combustion burner.
 8. The hot water supply apparatus as set forth in claim 6 wherein: a part of said exhaust gas pathway section and a part of said supply air pathway section are formed in the form of a double tube structure composed of an inner tube and an outer tube whereby said heat exchange with exhaust gas is performed.
 9. The hot water supply apparatus as set forth in claim 7 wherein: a part of said exhaust gas pathway section and a part of said supply air pathway section are formed in the form of a double tube structure composed of an inner tube and an outer tube whereby said heat exchange with exhaust gas is performed. 